Field of the Invention
The invention relates to a power breaker apparatus which performs energization and interception between a power source and a load.
Description of Related Art
A vehicle such as an automobile is equipped with a wide variety of loads (electronic equipment). In order to supply and intercept power to the loads, there is arranged a relay between a power supply such as a battery and loads. Recently, as the relay, instead of a conventional mechanical relay, there has been used a semiconductor switch.
For example, the patent document 1 (:JP-A-2007-295776) discloses a load circuit for supplying power to a load. This load circuit includes a battery, a semiconductor switch interposed between the battery and load, and a control circuit for turning on/off the semiconductor switch. The control circuit, when an overcurrent equal to or larger than a specific interception threshold value flows, detects it to turn off the semiconductor switch, thereby shutting off the circuit.
Meanwhile, when the load circuit is applied to an electric path through which a high current flows, there is a possibility that the high current can exceed the maximum current (rated current) which is allowed to flow through a single semiconductor switch. Thus, there is also known a method in which an electric path is equipped with an interception part constituted of a plurality of semiconductor switches connected in parallel to each other, and these semiconductor switches are driven in parallel. However, with this method, even when one of the semiconductor switches fails off, the threshold value current does not change; and thus, an excessive current flows in the remaining semiconductor switches that have not failed, thereby raising a possibility that they can be caused to fail.
In view of this, for example, the patent document 2 (:JP-A-2012-70045) discloses a load drive apparatus. In this load drive apparatus, there are provided a relay circuit group comprising multiple relay circuits connected in parallel to each other, each circuit including a semiconductor switch and a control circuit for controlling on/off of the semiconductor switch, and the relay circuit group is arranged in an electric path for connecting a power source and loads to each other. According to this structure, since, in every relay circuits, a current is detected and is compared with an interception threshold value, the above problem can be solved.
[Patent Document 1] JP-A-2007-295776
[Patent Document 2] JP-A-2012-70045
However, according to a related art, each parallel circuit must be equipped with a current detection device, which leads to higher cost and larger size of the apparatus. Also, since current detection and overcurrent check are performed in every parallel circuits, when switching on/off of the semiconductor switches, there is a possibility that an erroneous interception can be caused by the mismatch of a current flowing in the semiconductor switch. And, when trying to controllably suppress such erroneous interception, there is a possibility that the on/off control can be complicated.
One or more embodiments provide a power breaker apparatus which can suppress occurrence of erroneous interception with a simple structure and, even when one of semiconductor switches connected in parallel to each other fails, the remaining semiconductor switches can supply the minimum necessary power.
According to one or more embodiments, a power breaker apparatus which performs energization and interception between a power supply and a load, includes:
a current measuring part which measures a current value flowing in a power line supplying electric power from the power supply to the load;
an interception part disposed in the power line and including a plurality of semiconductor switches connected in parallel to each other;
a control part comparing the current value measured in the current measuring part with an interception threshold value, and controlling on/off of the plurality of the semiconductor switches according to a comparison result; and
a failure detection part which measures a potential on an output side of the interception part and detects a failure so that the control part checks for the failure of the semiconductor switches,
wherein the control part changes the interception threshold value from a normal value which is set when the failure is not determined in the semiconductor switches to an exceptional value for the failure of the semiconductor switches, when the failure of the semiconductor switches is determined according to a detection result of the failure detection part.
In the power breaker of one ore more embodiments, the normal value may be set according to energization conditions on the load side when all of the load is operated.
In the power breaker of one ore more embodiments, the interception part may further include a plurality of semiconductor switches connected in a forward direction in which a current flows through the power line from the load side to the power supply.
According to one or more embodiments, occurrence of erroneous interception of semiconductor switches connected in parallel to each other can be suppressed with a simple structure and, even when one of semiconductor switches connected in parallel to each other fails, the minimum necessary power can be supplied to a vehicle without destroying the remaining semiconductor switches.